WO-A-0250213 describes a process wherein different base oil grades are made in a so-called blocked-out mode. In this process a bottoms fraction of a hydrocracking process, which thus also yields middle distillates as products, is separated into various base oil precursor fractions. These fractions are subsequently catalytically dewaxed one after the other using a platinum-ZSM-5 based catalyst.
WO-A-9718278 discloses a process wherein up to 4 base oil grades, e.g. a 60N, 100N and 150N, are prepared starting from the bottoms fraction of a hydrocracker. In this process the bottoms fraction is first fractionated in a vacuum distillation into 5 fractions of which the heavier 4 fractions are further processed to different base oil grades by first performing a catalytic dewaxing followed by a hydrofinishing step.
A disadvantage of the above processes is that the process is not continuous. In other words the base oil grades are not made at the same time but sequential. This requires tankage for the intermediate products as obtained when the hydrocracker bottoms are fractionated and are awaiting their turn to be catalytically dewaxed. A further disadvantage are the mode switches which result in heating up of equipment and cooling of equipment causing deterionation of equipment. The mode switches also result in intermediate off-spec product every time a new grade is being processed. These slops need to be reprocessed or disposed off which is disadvantageous.
EP-A-649896 discloses a process to prepare a residue comprising a base oil by means of a process involving a hydrotreating step and a hydrocracking step on a heavy petroleum feedstock. The hydroprocessing steps yield a product from which middle distillates and a bottoms fraction (residue) are obtained. This bottoms fraction is subsequently solvent dewaxed to a single grade base oil grade.
WO 02/070627 discloses a process to prepare two or more base oil grades and a gas oil from a Fischer-Tropsch derived feed, i.e. not from a mineral crude derived feed.
EP-A-0 994 173 relates to a process for making an automatic transmission fluid composition.
U.S. Pat. No. 6,576,120 relates to a process for the catalytic dewaxing of a hydrocarbon feed containing waxy molecules.
WO-A-9723584 discloses a process wherein the bottoms fraction of a fuels hydrocracker is subjected to a catalytic dewaxing step. The dewaxed oil is partly recycled to the hydrocracking step and partly obtained as the lubricating base oil.
A disadvantage of the above process as described in WO-A-9723584 is that if more than one base oil grade is isolated from the dewaxed oil a large pour point distribution occurs. In other words the resulting the lower viscous base oil grades will have a too low pour point. This pour point give away, or difference with the desired value, is indicative for yield loss of said lower viscous base oil grade.